Review ArticlesFever Without Source in Unvaccinated Children Aged 3 to 24 Months What Workup Is Recommended?Finkel, Leah MD∗; Ospina-Jimenez, Camila MD†; Byers, Michael MD‡; Eilbert, Wesley MD§ Author Information From the ∗Departments of Emergency Medicine and Pediatrics †Department of Pediatrics, University of Illinois at Chicago College of Medicine ‡Department of Pediatrics, John H. Stroger Jr. Hospital §Department of Emergency Medicine, University of Illinois at Chicago College of Medicine, Chicago, IL. Disclosure: The authors declare no conflict of interest. Reprints: Wesley Eilbert, MD, Department of Emergency Medicine, University of Illinois at Chicago, College of Medicine, Rm 469 COME, 1819 W. Polk St., Chicago, IL 60612 (e-mail: [email protected]). Pediatric Emergency Care 37(12):p e882-e885, December 2021. | DOI: 10.1097/PEC.0000000000002249 Buy Metrics Abstract Fever is the most common complaint for infants and children brought to the emergency department. Most febrile children younger than 3 years will have a clinically apparent source of infection. However, in approximately 20% of these children, a source cannot be identified by history and physical examination alone. The recommended diagnostic approach to children younger than 3 years presenting with fever without source (FWS) has changed dramatically over the past 30 years because of the widespread use of the Haemophilus influenza type b and polyvalent pneumococcal vaccines. The percentage of children in the United States unvaccinated at 24 months is now over 1% and seems to be increasing. This article will review what is currently known about FWS in children aged 3 to 24 months in the modern era and how it pertains to unvaccinated children treated in the emergency department. An algorithm for the treatment of unvaccinated young children presenting with FWS is proposed. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.